1. Field of the Invention
The present invention generally relates to ink jet printhead apparatus and, more particularly, to an integrated multi-color drop-on-demand type ink jet printhead having longitudinally extending sidewall actuators.
2. Description of Related Art
Ink jet printing systems use the ejection of tiny droplets of ink to produce an image. The devices produce highly reproducible and controllable droplets, so that a droplet may be printed at a location specified by digitally stored image data. Most ink jet printing systems commercially available may be generally classified as either a "continuous jet" type ink jet printing system where droplets are continuously ejected from the printhead and either directed to or away from the paper depending on the desired image to be produced or as a "drop-on-demand" type ink jet printing system where droplets are ejected from the printhead in response to a specific command related to the image to be produced.
In drop-on-demand type ink jet printing systems, a volumetric change in the fluid is induced by the application of a voltage pulse to a piezoelectric material which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid and these are directed so as to produce a droplet that issues from an orifice. Recently, considerable interest has been directed to piezoelectric drop-on-demand type ink jet printheads which utilize sidewall actuators to impart droplet ejecting pressure pulses into the ink carrying channels. See, for example, U.S. Pat. Nos. 4,536,097 to Nilsson, 4,879,568 to Bartky et al., 4,887,100 to Michaelis et al. and 5,016,028 to Temple.
In Ser. No. 07/748,220, a U type drop-on-demand ink jet printhead was disclosed. The U type ink jet printhead included a lower body portion formed from an active piezoelectric material, a plurality of intermediate sections formed from an active piezoelectric material and an upper body portion formed from an inactive material. The lower body portion further included an upper side surface and a plurality of generally parallel spaced projections vertically projecting therefrom. Lower side surfaces of a plurality of intermediate sections were conductively mounted to top side surfaces of the lower body projections and the upper body portion was conductively mounted to upper side surfaces of the plurality of intermediate sections. In this manner, an ink jet printhead in which the lower body portion, the plurality of intermediate sections and the upper body portion defined a plurality of generally parallel, longitudinally extending ink ejecting channels was formed. For this ink jet printhead, the intermediate sections further defined first and second actuators and the projections and upper surface of the lower body portion defined a third actuator for each of the channels.
Like most other previously disclosed ink jet printing systems, the aforementioned configuration for an ink jet printhead provides for only one fluid system and is, therefore, capable of printing in only one color, most commonly, black. Color printing, however, requires multiple ink colors. For example, the use of four ink colors--the primary colors (yellow, magenta and cyan) and black-has proven quite satisfactory for producing color images. When manufacturing multiple color ink jet printheads, the most common approach has been to produce a printing system having a separate printhead for each ink color. However, there are numerous difficulties which arise when using multiple printheads in a single ink jet printing system.
Of primary concern is the requirement that the separate printheads must be properly aligned (or "registered") with each other in order for the printing system to properly produce color images. Furthermore, as ink jet printheads must be readily replaceable, permanently fastening the ink jet printheads after registration is not a feasible solution to this problem. Thus, in order to achieve registration of the separate printheads, some type of alignment capability which allows the printing system to determine the pitch and position of each printhead and make appropriate adjustments must be incorporated into the printing system. For example, it is contemplated that control software may be used to maintain proper registration of each printhead in such a printing system. However, not only is it difficult to ensure that such systems always accurately align the printheads, they add considerable cost and complexity to multi-color ink jet printing systems.
Furthermore, the use of multiple printheads in multi-color printing systems represents a significant obstacle to the production of smaller, less expensive multi-color ink jet printers. Each printhead is an independent system which requires its own transport, ink supply and actuation mechanisms. Thus, there are numerous redundant systems in a multiple printhead multi-color ink jet printer which, due to the independent nature of each printhead, resists integration. As a result, each printhead demands a significant amount of space, thereby impeding the successful construction of a compact, multi-color ink jet printhead.
It is, therefore, an object of this invention to provide an ink jet printhead which integrates multiple fluid systems in a single assembly, thereby permitting the manufacture of a multi-color ink jet printhead.